This process relates to the production of light, high strength columns, masts or spars such as but not limited to those used in the sailboat industry, using fibre reinforced plastics such as carbon, Kevlar and glass fibres, impregnated with a bonding resin such as epoxy or polyester.
In general, fibre reinforced masts or spars such as those used in the sailboat industry are wound or moulded around a male mould or mandrel and require finishing on the outside which is labour intensive and therefore expensive. Alternatively, they are hand laid up as two or more separate parts using female moulds and later bonded longitudinally to form the closed section, a time consuming process that requires careful control to produce reliable bonded joints. In addition, both methods usually employ vacuum bagging and heat curing in large ovens or autoclaves further adding to the cost of production. (See document D1, section entitled Process and Development, in which the xe2x80x9ctwo part female mouldxe2x80x9d method described is the closest to my method.)
My single, concave or xe2x80x9cUxe2x80x9d shaped, female mould method overcomes many of these problems by enabling the part to be moulded by the hand lay-up method or other conventional methods using cold or hot cure resins and makes it easy to vary the thickness, orientation and composition of the moulding without affecting the outside dimensions of the finished part.
The cross-section of the concave female mould required that will ultimately produce a closed finished section of the desired shape can be easily predetermined by calculation, trial and error, or more usually a combination of the two.
The single join required to produce the closed section is also relatively easy to effect and can be done in a number of different ways, some of which are illustrated here. In addition, before the cured part is clamped closed and bonded, inserts and backing plates can be bonded or fastened to the inside of the section to absorb localised loads that might be caused by fittings and fastenings such as spreaders, tangs, tracks or sheaves in the case of sailboat masts. Additional pieces such as conduit for wiring can also be added at this stage.
Furthermore, if a coloured gel-coating is used against the mould surface, the part will not require painting and in the example illustrated will need only a small amount of finishing work along one edge of the bonded joint. Alternatively, a sail track or similar, that is to be fastened over the joint can be so shaped as to hide the unfinished edge further reducing finishing time.
Yet another advantage of this method, is that the clamping together of the xe2x80x9cUxe2x80x9d section pre-stresses the walls thereby increasing their resistance to buckling.
D1: C-Spars (U.K.): Section entitled Process and Development, source: www.c-spars.uk.com/